The present invention relates to an electric power supply apparatus which is to be mounted on a vehicle, and more particularly to a technique of improving the safety during maintenance.
Recently, attempts to increase the voltage of a battery which is to be mounted on a vehicle and use a power supply of about 36 volts in place of a 12-volt power supply that is conventionally used have been made. In the case where a 36-volt battery is used, a system in which 36-volt and 12-volt loads are mixedly used because it is difficult to change standards of all of various loads to be mounted on a vehicle to those suitable for 36 volts, and the 12-volt loads are driven by a voltage that is obtained by converting 36 volts DC into 12 volts is employed.
FIG. 11 is a circuit diagram showing a conventional example of such a power supply apparatus. As shown in the figure, in the power supply apparatus 101, an AC voltage output from a generator (M/G) 102 is converted into a DC voltage by a rectifier (AC/DC) 103. An output terminal of the rectifier 103 is connected to a 36-volt load 104, a 36-volt battery 105, and a DC/DC converter 106 via junction boxes (J/B) 107 and 108.
The DC/DC converter 106 converts a DC voltage of 36 volts into a DC voltage of 12 volts. An output terminal of the converter is connected to a 12-volt battery 110 and a 12-volt load 111 via a junction box 109.
According to the configuration, the AC voltage output from the generator 102 is converted into a DC voltage of 36 volts by the rectifier 103, and then supplied to the 36-volt load 104 and the 36-volt battery 105. Therefore, the 36-volt load 104 can be driven and the 36-volt battery 105 can be charged.
Thereafter, the voltage is lowered to 12 volts by the DC/DC converter 106. The voltage of 12 volts is supplied to the 12-volt load 111 and the 12-volt battery 110, so that the 12-volt load 111 can be driven and the 12-volt battery 110 can be charged.
In the conventional power supply apparatus 101, there is a case where, when a power supply wire through which the DC/DC converter 106 is to be coupled to the battery 105 or 110 is connected to or disconnected from the battery, an arc (spark) is generated in a connecting portion. For example, an arc may be generated in the following situations.
(A) When a connection is made or broken in such a connecting portion under a voltage applied state (on-load state), an arc is generated in the portion. The arc is greater in degree as the voltage is higher.
(B) In the case where the DC/DC converter 106 is not used for a long time period or is initially operated, an internal capacitor of the DC/DC converter 106 has a charging voltage of about 0 volt. In such a case, when a power supply wire is connected to the converter, a current of the voltage of the 36-volt battery 105 is flown into the internal capacitor. When the power supply wire is in contact with a terminal, therefore, an arc is generated. The arc is greater in degree as the 36-volt battery is closer to a fully charged state.
(C) In the case where the DC/DC converter 106 has been operated even once, the internal capacitor of the DC/DC converter 106 sometimes remains to be charged by a certain voltage. In such a case, when a terminal of a power supply wire which is connected to the plus terminal of the DC/DC converter 106 is in contact with the vehicle body or another metal part during a work of disconnecting the power supply wire, a short circuit occurs and an arc is generated. In the case where a power supply wire is first connected to the 36-volt battery 105, when the power supply wire is then connected to the DC/DC converter 106, an arc is generated. By contrast, in the case where a power supply wire is first connected to the DC/DC converter 106, when the power supply wire is then connected to the 36-volt battery 105, an arc is generated.
As described above, in the conventional power supply apparatus 101, there is a problem that an arc is generated during a work of connecting or disconnecting a power supply wire in maintenance of the DC/DC converter 106 which is disposed between the high-voltage side (36-volt side) and the low-voltage side (12-volt side).
The invention has been conducted in order to solve the problem of the conventional art. It is an object of the invention to provide an in-vehicle electric power supply apparatus in which arc generation can be prevented from occurring during a work of connecting or disconnecting a power supply wire that is used between a DC/DC converter and a battery.
(1) In order to attain the object, the invention is characterized in that, in an in-vehicle electric power supply apparatus having: a DC/DC converter for voltage conversion; a power supply circuit which is disposed on a high-voltage side of the DC/DC converter; and a power supply circuit which is disposed on a low-voltage side of the DC/DC converter, an arc preventing unit is disposed between the DC/DC converter and at least one of the power supply circuits, when the DC/DC converter and the power supply circuit are to be connected to each other, the arc preventing unit controls the connection to be performed via a high-resistance circuit of a first resistance, and thereafter changes the connection to be performed via a low-resistance circuit of a second resistance which is lower than the first-resistance, and when the DC/DC converter and the power supply circuit are to be disconnected from each other, the arc preventing unit controls the DC/DC converter to discharge a charging voltage of a capacitor of the DC/DC converter.
(2) The invention is characterized also in that, in an in-vehicle electric power supply apparatus having: a DC/DC converter for voltage conversion; a power supply circuit which is disposed on a high-voltage side of the DC/DC converter; and a power supply circuit which is disposed on a low-voltage side of the DC/DC converter, an arc preventing unit is disposed between the DC/DC converter and at least one of the power supply circuits, and the arc preventing unit has: a first circuit configured by a series connection of a first switch and a first resistor; a second switch which is connected in parallel with the first circuit; a second circuit which is configured by a series circuit of a third switch and a second resistor, and which is connected across terminals of a capacitor of the DC/DC converter; and a controlling unit for, when the DC/DC converter and the power supply circuit are to be connected to each other, controlling the first switch to be turned on, and then controlling the first switch to be turned off and the second switch to be turned on, and for, when the DC/DC converter and the power supply circuit are to be disconnected from each other, controlling the second switch to be turned off and the third switch to be turned on.
(3) The invention is characterized also in that the controlling unit controls the first switch to be turned on when a voltage VB which is applied to a connection terminal of the DC/DC converter is equal to or higher than a first threshold Vth1 after the connection terminal of the DC/DC converter is connected to an output terminal of the power supply circuit, and controls the first switch to be turned off, and the second switch to be turned on when a difference between the voltage VB and a terminal voltage VC of the capacitor of the DC/DC converter is equal to or lower than a second threshold Vth2.
(4) The invention is characterized also in that, when a vehicle ignition is turned off, the controlling unit controls the second switch to be turned off, and then controls the third switch to be turned on.
(5) The invention is characterized also in that, when the terminal voltage VC of the capacitor of the DC/DC converter is equal to or lower than a third threshold Vth3 after the third switch is turned on, the controlling unit controls the third switch to be turned off.
(6) The invention is characterized also in that the apparatus further has an informing unit which, when the third switch is turned on, informs of the turn-on state.